Method and apparatus for supporting self-optimisation in a wireless communication system

ABSTRACT

The present disclosure relates to a communication method and system for converging a 5th-Generation (5G) communication system for supporting higher data rates beyond a 4th-Generation (4G) system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services. The present disclosure provides a method for supporting self-configuration and self-optimization in a wireless communication system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 17/090,810,filed Nov. 5, 2020, which is based on and claims priority to ChinesePatent Application No. 201911089876.7 filed on Nov. 8, 2019, ChinesePatent Application No. 202010091347.7 filed on Feb. 13, 2020, andChinese Patent Application No. 202010276154.9 filed on Apr. 9, 2020, thedisclosures of which are herein incorporated by reference in theirentirety.

BACKGROUND 1. Field

The present disclosure relates to a wireless communication technology,and in particular, to a method and a device for supportingself-configuration and self-optimization.

2. Description of Related Art

To meet the demand for wireless data traffic having increased sincedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a ‘Beyond 4G Network’ or a‘Post UE System’. The 5G communication system is considered to beimplemented in higher frequency (mmWave) bands, e.g., 60 GHz bands, soas to accomplish higher data rates. To decrease propagation loss of theradio waves and increase the transmission distance, the beamforming,massive multiple-input multiple-output (MIMO), Full Dimensional MIMOMIMO), array antenna, an analog beam forming, large scale antennatechniques are discussed in 5G communication systems. In addition, in 5Gcommunication systems, development for system network improvement isunder way based on advanced small cells, cloud Radio Access Networks(RANO, ultra-dense networks, device-to-device (D2D) communication,wireless backhaul, moving network, cooperative communication,Coordinated Multi-Points (CoMP), reception-end interference cancellationand the like. In the 5G system, Hybrid FSK and QAM Modulation (FQAM) andsliding window superposition coding (SWSC) as an advanced codingmodulation (ACM), and filter bank multi carrier (FBMC), non-orthogonalmultiple access (NOMA), and sparse code multiple access (SCMA) as anadvanced access technology have been developed.

The Internet, which is a human centered connectivity network wherehumans generate and consume information, is now evolving to the Internetof Things (IoT) where distributed entities, such as things, exchange andprocess information without human intervention. The Internet ofEverything (IoE), which is a combination of the IoT technology and theBig Data processing technology through connection with a cloud server,has emerged. As technology elements, such as “sensing technology”,“wired/wireless communication and network infrastructure”, “serviceinterface technology”, and “Security technology” have been demanded forIoT implementation, a sensor network, a Machine-to-Machine (M2M)communication, Machine Type Communication (MTC), and so forth have beenrecently researched. Such an IoT environment may provide intelligentInternet technology services that create a new value to human life bycollecting and analyzing data generated among connected things. IoT maybe applied to a variety of fields including smart home, smart building,smart city, smart car or connected cars, smart grid, health care, smartappliances and advanced medical services through convergence andcombination between existing Information Technology (IT) and variousindustrial applications.

In line with this, various attempts have been made to apply 5Gcommunication systems to loT networks. For example, technologies such asa sensor network, Machine Type Communication (MTC), andMachine-to-Machine (M2M) communication may be implemented bybeamforming, MIMO, and array antennas. Application of a cloud RadioAccess Network (RAN) as the above-described Big Data processingtechnology may also be considered to be as an example of convergencebetween the 5G technology and the IoT technology.

Modern mobile communication increasingly tends to provide a user withmultimedia services which are transmitted at a high rate. FIG. 1 shows asystem architecture diagram of system architecture evolution (SAE).

A user equipment (UE) 101 is a terminal device used to receive data.Evolved universal terrestrial radio access network (E-UTRAN) 102 is aradio access network in which a macro base station (eNodeB/NodeB) forproviding the UE with an interface for access to the radio network isincluded. A mobility management entity (MME) 103 is responsible formanaging a mobility context, a session context and security informationof the UE. A service gateway (SGW) 104 mainly provides a function of auser plane, and the MME 103 and the SGW 104 may be within the samephysical entity. A packet data network gateway (PGW) 105 performsfunctions such as charging, lawful interception and the like, and thePGW and the SGW 104 may be within the same physical entity. A policy andcharging rules function entity (PCRF) 106 provides quality-of-service(QoS) policies and charging criteria. A general packet radio servicesupport node (SGSN) 108 is a network node device for providing routingfor data transmission in a universal mobile telecommunications system(UMTS). A home subscriber server (HSS) 109 is the UE's home subsystemand is responsible for protecting user information including a currentlocation of the user equipment, an address of the service node, usersecurity information, a packet data context of the user equipment, andthe like.

FIG. 2 shows a system architecture diagram of a next-generation networkor a fifth-generation (5G) network.

A user equipment (UE) 201 is a terminal device used to receive data. Anext generation-Radio Access Network (NG-RAN) 202 is a radio accessnetwork in which a base station (a gNB or an eNB connected to the 5GCore network (5GC), the eNB connected to the 5GC being also calledng-gNB) for providing the UE with an interface for access to the radionetwork is included. An access and mobility management function entity(AMF) 203 is responsible for managing mobility context and securityinformation of the UE. A user plane function entity (UPF) 204 mainlyprovides a function of a user plane. A session management functionentity (SMF) 205 is responsible for session management. A data network(DN) 206 includes, for example, operator's services. Internet access,third-party services, and the like.

Support for mobility robustness self-optimization (MRO) in the 5G systembegin to be discussed in release 16. The MRO includes intra-systemmobility robustness self-optimization and inter-system mobilityrobustness self-optimization (such as mobility robustnessself-optimization in movement or handover between 5G system and 4Gsystem). Currently, the intra-system mobility robustnessself-optimization procedure may be performed based on a radio resourcecontrol (RRC) connection re-establishment request message or based on aradio link failure (RLF) report of the UE. For the method performedbased on the RLF report the UE, the method is currently performedaccording to the following steps: a UE fails due to a radio link failureor a handover failure; the UE reconnects to a cell, and the UEindicates, to the newly accessed base station, the RLF report isavailable; the base station requests the UE to report the UE RLF report;after receiving the UE RLF report, the base station knows, from the RLFreport, the cell identity of the cell that last serves the UE prior tothe failure; the base station transmits the UE RLF report to the basestation which controls the cell that last serves the UE prior to thefailure; the base station which controls the cell that last serves theUE prior to the failure determines the cause of the failure occurring,such as too early handover, too late handover, or handover to wrongcell; if the cause is the too early handover or the handover to wrongcell, the base station which controls the cell that last serves the UEprior to the failure transmits the handover report to the base stationthat triggers the too early handover or the handover to wrong cell.

SUMMARY

For the 5G intra-system handover, there are the intra-radio accesstechnology (RAT) handover and the inter-RAF handover. Whether the abovemechanism may be applied to the intra-system inter-RAT has not beendiscussed in detail.

The present disclosure provides several mechanisms for supporting theinter-RAT MIRO in order to address the problem about mobility robustnesswhen a UE moves or handovers between different RATs.

According to an aspect of the present disclosure, there is provided amethod performed by a terminal in a wireless communication system, andthe method includes: storing information on a connection failure, incase that the connection failure in a cell of a first base stationrelated to a first radio access technology (RAT) is detected;establishing a connection with a second base station related to a secondRAT; receiving, from the second base station, a request messageincluding information for indicating the terminal to report theinformation on the connection failure; and transmitting, to the secondbase station, a response message including the information on theconnection failure to be transferred to the first base station, based onthe request message.

According to another aspect of the present disclosure, there is provideda method performed by a second base station related to a second radioaccess technology (RAT) in a wireless communication system, and themethod includes: establishing a connection with a terminal;transmitting, to the terminal, a request message including informationfor indicating the terminal to report information on a connectionfailure; receiving, from the terminal, a response message including theinformation on the connection failure in a cell of a first base stationrelated to a first RAT, based on the request message; and transferringthe information on the connection failure to the first base station.

According to another aspect of the present disclosure, there is provideda terminal in a wireless communication system, and the terminalincludes: a transceiver; and a controller operably connected to thetransceiver, the controller configured to: store information on aconnection failure, in case that the connection failure in a cell of afirst base station related to a first radio access technology (RAT) isdetected, establish a connection with a second base station related to asecond RAT, receive, from the second base station via the transceiver, arequest message including information for indicating the terminal toreport the information on the connection failure, and transmit, to thesecond base station via the transceiver, a response message includingthe information on the connection failure to be transferred to the firstbase station, based on the request message.

According to another aspect of the present disclosure, there is provideda second base station related to a second radio access technology (RAT)in a wireless communication system, and the second base stationincludes: a transceiver; and a controller operably connected to thetransceiver, the controller configured to: establish a connection with aterminal; transmit, to the terminal via the transceiver, a requestmessage including information for indicating the terminal to reportinformation on a connection failure, receive, from the terminal via thetransceiver, a response message including the information on theconnection failure in a cell of a first base station related to a firstRAT, based on the request message, and transfer the information on theconnection failure to the first base station.

According to another aspect of the present disclosure, there is provideda method for supporting self-configuration and self-optimization, andthe method includes steps as follows.

A failure occurs for the UE in cell A of a base station 1;

The UE re-establishes the RRC connection in a cell of a base station 2.In the RRC connection establishment completion or RRC connectionre-establishment completion message, the UE indicates to the network theRLF report information is available.

The base station 2 requests the UE to report the RLF report, and the UEtransmits the UE RLF report to the base station 2. For the UE, in themessage for transmitting the UE RLF report (outside the UE RLF reportcontainer), the cell identity of the last cell that served the UE priorto the failure occurred is also included and/or TAC or TAI for thiscell, Each of the above cell identities may be a global cell identity ora PCI and frequency information.

The base station 2 transmits a failure indication message to the basestation 1. The failure indication message includes the RLF reportreceived from the UE.

The base station 1 detects the cause of the failure;

For too early handover or handover to wrong cell, the base station 1transmits a handover report message to the base station which controlsthe source cell that triggers the last handover.

This method may enable the network to correctly detect the cause of thefailure in the case that the UE fails when moving between differentRATs, while reducing the time for the UE to store RLF report informationand reducing the process on the base station side, that is, the NR basestation does not need to decode (or parse) the content of the LTE RRCand the LTE base station does not need to parse the content of the NRRRC.

According to another aspect of the present disclosure, there is providedanother method for supporting self-configuration and self-optimization,and the method includes steps as follows:

A UE fails in a cell of a base station 1

The UE re-establishes the RRC connection in a cell of a base station 2of a different radio access type from that of the base station 1.

The UE is connected to the base station 3 of the same radio access typeas that of the base station 1. In the RRC connection establishmentcompletion or RRC connection re-establishment completion or RRCreconfiguration completion message, the UE indicates to the network theRLF report information is available.

The base station 3 requests the UE to report the RLF report, and the UEtransmits the UE RFL report to the base station 3. The RLF reportincludes cell identity of cell where the UE successfully establishes theRRC connection or cell identity of cell where the UE attempts toestablish the RRC connection, after the failure; the time elapsed fromthe failure to the RRC reconnection attempt the or the successful accessto the network.

The base station 3 transmits a failure indication message to the basestation 1. The failure indication message includes the RLF reportreceived from the UE.

The base station 1 checks the cause of the failure occurring.

For too early handover or handover to wrong cell, the base station 1transmits a handover report message to the base station which controlsthe source cell that triggers the last handover.

TECHNICAL EFFECT

From the description of the method for supporting self-configuration andself-optimization of the present disclosure, the method enables thenetwork to correctly detect the cause of the failure in the case thatthe UE fails when moving between different RATs, while reducing the timefor the UE to store RLF report information and reducing the process onthe base station side, that is, the NR base station does not need todecode the content of the LTE RRC and the LTE base station does not needto decode the content of the NR RRC. When there is no Xn interfacebetween the base station which controls the cell where the failureoccurs and the base station which controls the cell where the UEreconnects, the base station may still transmit the RLF report to thebase station which controls the cell where the failure occurs throughthe core network without parsing the RLF of other radio accesstechnologies. When there is no Xn interface between the base stationwhich controls the cell where the failure occurs and the base stationwhich controls the cell that triggers the last handover, the basestation which controls the cell where the failure occurs may stilltransmit a handover report to the base station which controls the sourcecell that triggers the last handover.

This method may enable the network to correctly detect the cause of thefailure in the case that the UE fails when moving between differentRATs, while reducing the process on the base station side, that is, theNR base station does not need to decode the content of the LTE RRC andthe LTE base station does not need to decode the content of the NR RRC.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.

Moreover, various functions described below can be implemented orsupported by one or more computer programs, each of which is formed fromcomputer readable program code and embodied in a computer readablemedium. The terms “application” and “program” refer to one or morecomputer programs, software components, sets of instructions,procedures, functions, objects, classes, instances, related data, or aportion thereof adapted for implementation in a suitable computerreadable program code. The phrase “computer readable program code”includes any type of computer code, including source code, object code,and executable code. The phrase “computer readable medium” includes anytype of medium capable of being accessed by a computer, such as readonly memory (ROM), random access memory (RAM), a hard disk drive, acompact disc (CD), a digital video disc (DVD), or any other type ofmemory. A “non-transitory” computer readable medium excludes wired,wireless, optical, or other communication links that transporttransitory electrical or other signals. A non-transitory computerreadable medium includes media where data can be permanently stored andmedia where data can be stored and later overwritten, such as arewritable optical disc or an erasable memory device.

Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1 is a system architecture diagram of system architecture evolution(SAE);

FIG. 2 is a schematic diagram of an initial overall architecture for the5G technology;

FIG. 3 illustrates a first method for supporting self-configuration andself-optimization according to the present disclosure;

FIG. 4 illustrates a second method for supporting self-configuration andself-optimization according to the present disclosure;

FIG. 5 illustrates a third method for supporting self-configuration andself-optimization according to the present disclosure;

FIG. 6 illustrates a first embodiment of the first method for supportingself-configuration and self-optimization according to the presentdisclosure;

FIG. 7 illustrates a second embodiment of the first method forsupporting self-configuration and self-optimization according to thepresent disclosure;

FIG. 8 illustrates a first embodiment of the third method for supportingself-configuration and self-optimization according to the presentdisclosure;

FIG. 9 is a block diagram of a terminal according to an embodiment thepresent disclosure; and

FIG. 10 is a block diagram of a base station according to an embodimentof the present disclosure.

DETAILED DESCRIPTION

FIGS. 1 through 10 , discussed below, and the various embodiments usedto describe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged system or device.

The method for supporting self-configuration and self-optimizationprovided by the present disclosure may address the problem aboutmobility robustness when a UE moves or handovers between differentRAT's, reduce the time for the UE to store the RLF report, and avoid theproblem that base stations of different radio access technologiesunderstand each other's RRC message, which ensures that failure eventsbetween different RATS are found timely so that the aim ofself-configuration and self-optimization is achieved.

A first method for supporting self-configuration and self-optimizationaccording to the present disclosure is illustrated as FIG. 3 . Adetailed description of steps which are not related to the presentdisclosure is omitted here. In the method, base station 1 and basestation 2 may be base stations of different radio access technologies.For example, the base station 1 is an ng-eNB or an eNB that supports theLTE air interface technology, and the base station 2 is a gNB thatsupports the NR radio access technology. Alternatively, the base station1 is a gNB that supports the NR radio access technology, and the basestation 2 is an ng-eNB or an eNB that supports the UE air interfacetechnology. The base station 3 may be a base station that supports anyradio access technology, for example, the same radio access technologyas that supported by the base station 1, the same radio accesstechnology as that supported by the base station 2, or other radioaccess technologies. The method includes steps as follows.

Step 301: A UE fails in a cell of the base station 1, and it is assumedthat the UE fails in the cell A. A failure here may be an RLF or ahandover failure. For the handover failure, the cell A is a target cellfor the handover. The cell where the failure occurs is also the cellthat last serves the UE prior to the failure. The UE stores (or saves)one or more of the following information:

-   -   Cell identity of the cell A, which may be a global cell identity        or a physical cell identifier (PCI) and frequency information;    -   Tracking area code (TAC) or tracking area identity (TAI) of the        cell A;    -   Cell identity of the source cell that triggers the last        handover;    -   TAC or TAI of the source cell that triggers the last handover;    -   Time elapsed from the beginning of the last handover to the        failure;    -   Connection failure being an RLF or a handover failure;    -   Radio measurements of the UE;    -   C-RNTI allocated to the UE by the cell that last serves the UE        prior to the failure;    -   Cause of triggering an RLF;    -   Cell identity of the cell where the UE attempts to re-establish        the RRC connection, or cell identity of the cell where the UE        attempts to establish the RRC connection, or cell identity of        the cell where the UE establishes the RRC connection, after the        failure;    -   Time elapsed from the failure to the UE RLF report.

The last two items may be stored (or saved) in a subsequent procedure.For example, when the UE attempts to re-establish the RRC connection,the LTE records the cell identity of the cell where the UE attempts tore-establish the RRC connection after the failure. When the UE preparesto transmit the RLF report, the UE records the time elapsed from thefailure to the UE RLF report.

All the above cell identities may be the global cell identity or the PCIand the frequency information.

The UE also stores the RLF report of which radio access technology thestored RLF report information is, such as an LTE RLF report or an NR RLFreport.

If the base station 1 is an LTE base station (for example, an ng-eNB oran eNB), the above RLF report information is the LTE RLF report, whichis in the format and encoding of the LTE RRC.

If the base station 1 is an NR base station (for example, a gNB), theabove-mentioned RLF report information is the NR RLF report, which is inthe format and encoding of the NR RRC.

Step 302: The UE re-establishes the RRC connection in a cell of the basestation 2. The UE may re-establish the RRC connection through the RRCconnection establishment or RRC connection re-establishment procedure.In the RRC connection establishment completion or RRC connectionre-establishment completion message, the UE indicates, to the network,that the RLF report information is available. The UE may indicate, tothe network, that the RLF report information is available. The UE mayalso indicate, to the network, that the RLF report information of whichradio access technology is available, for example, the UE indicates, tothe network, that the LTE RLF report or the NR RLF report is available.The UE may also indicate, to the network, the LTE RLF report and the NRRLF report are available.

The method of the present disclosure may further include the step of:broadcasting, by the base station, whether the base station supports theRLF information reporting, or broadcasting, by the base station, the RLFinformation reporting of which radio access technology the base stationsupports. For example, the LTE base station broadcasts whether the LTEbase station supports the NR RLF information reporting and/or the LTERLF information reporting, and the NR base station broadcasts whetherthe NR base station supports the LTE RFL information reporting and/orthe NR RLF information reporting. If the base station with which the UEre-establishes the RRC connection supports the RLF informationreporting, or supports the information reporting of the correspondingradio access technology stored by the UE, the UE transmits, to there-accessed base station, that the RLF information reporting or the RLFinformation reporting of which radio access technology is available. Forexample, the UE may indicate to the base station that the RLFinformation reporting to the base station is available, and the UE mayalso indicate that the NR RLF information reporting or the LTE RLFinformation reporting to the base station is available.

If the base station 2 is the NR base station gNB, and the UE stores theLTE RLF report, the UE indicates, to the base station 2, that the RLFreport information is available, through the RRC connectionestablishment completion or RRC connection re-establishment completionmessage of the NR. The UE may indicate that the RLF report informationis available to the base station 2 through the RRC connectionestablishment completion or RRC connection re-establishment completionmessage of the NR. The UE may also indicate, to the base station 2, theRFL report information of which radio access technology is available,for example, the UE indicates, to the base station 2, that the LTE RLFreport or the NR RFL report is available. The LTE may also indicate, tothe base station 2, that the LTE RFL report and the NR RLF report areavailable.

If the base station 2 is the LTE base station ng-eNB or eNB, and the LTEstores the NR RLF report, the UE indicates, to the base station 2, thatthe RLF report information is available, through the RRC connectionestablishment completion or RRC connection re-establishment completionmessage of the LTE. The UE may indicate that the RLF report informationis available to the base station 2 through the RRC connectionestablishment completion or RRC connection re-establishment completionmessage of the LTE. The UE may also indicate, to the base station 2, theRLF report information of which radio access technology is available,for example, the UE indicates, to the base station 2, that the RLFreport or the NR RLF report is available. The UE may also indicate, tothe base station 2, that the LTE RLF report and the NR RLF report areavailable.

Step 303: The base station 2 requests the UE to report the RFL report,and the UE transmits the LTE RLF report to the base station 2.

The base station 2 may also indicate, to the UE, the RLF report of whichradio access technology is requested. For example, the base station 2requests the UE to report the LTE RFL report or the NR RLF report. Thebase station 2 may also request the UE to report the LTE RLF report andthe NR RLF report. The base station 2 requests the UE to report the RLFreport according to the RFL report being available or the RLF report ofwhich radio access technology being available indicated by the UE in theRRC connection establishment completion or RRC connectionre-establishment completion message. For example, if the LTE indicatesthat the LTE RLF report is available, and the base station 2 supportsthe request for the LTE report, the base station 2 may request the UE toreport the LTE RLF report. If the UE indicates that the NR RLF report isavailable, and the base station 2 supports the request for the NRreport, the base station 2 may request the UE to report the NR RLFreport.

Alternatively, the base station does not need to distinguish between theradio access technologies. The UE indicates that the RLF report isavailable, and then the base station requests the UE to report the RLFreport.

The base station may request the UE RLF report through a UE informationrequest message. The UE information request may include the RLF reportof which radio access technology is requested, for example, the NR RLFreport is requested or the LTE RLF report is requested.

The UE may transmit the RLF report to the base station through a UEinformation response message. The UE information response messageincludes the RLF report. The RLF report may be the LTE RLF report and/orthe NR RLF report.

The LTE RLF report includes the content described in step 301. In the UERLF report, the cell identity of the cell that last serves the UE beforethe failure occurs may be included. In the message of transmitting theUE RLF report (outside the UE RLF report container), the cell identityof the cell that last serves the UE before the failure occurs is alsoincluded. The cell that last serves the UE prior to the failure is alsothe cell where the failure occurs. For the handover failure, the cell isa target cell in a target base station. All the cell identities may bethe global cell identity or the PCI and frequency information. In thepresent embodiment, the cell is cell A.

In the UE RLF report, the TAC or TAI of the cell that last serves the UEbefore the failure occurs is included. In the message of transmittingthe UE RLF report (outside the UE RLF report container), the TAC or TAIof the cell that last serves the UE before the failure occurs is alsoincluded. The cell that last serves the UE prior to the failure is alsothe cell where the failure occurs. For handover failure, the cell is thetarget cell in the target base station. In the present embodiment, thecell is cell A.

If the base station 1 is the LTE base station and the base station 2 isthe NR base station, the UE make the LTE RLF report information beincluded in the NR RRC message, and make the cell identity of the cellthat last serves the UE before the failure occurs and/or the TAC or TAIof the cell also be included in the NR RRC message (outside the LTE RLFreport container) at the same time.

If the base station 1 is the NR base station and the base station 2 isthe base station, the UE make the NR RLF report information be includedin the LTE RRC message, and the cell identity of the cell that lastserves the UE before the failure occurs and/or the TAC or TAI of thecell also be included in the LTE RRC message (outside the NR RLF reportcontainer).

Step 304: The base station 2 knows the cell that last serves the UEprior to the failure according to the cell identity of the cell thatlast serves the UE before the failure occurs included in the RRCmessage. Here, the cell that last serves the UE prior to the failure iscontrolled by the base station 1. The base station 2 transmits a failureindication message to the base station 1. The failure indication messageincludes the RLF report received from the UE.

If there is no Xn interface between the base station 2 and the basestation 1, the base station 2 needs to transmit the failure indicationmessage to the base station 1 through the core network. The base station2 knows the TAI of the cell of the base station 1 from the cell identityof the cell that last serves the UE before the failure occurs and theTAC or TAI of the cell included in the RRC message. The base station 2transmits a message to the core network, and the message includes the UERLF report and the TAI of the cell in which the failure occurs. The TAIis used for routing in the core network, for example, the TAI is used bycore network entity 2 (such as AMF2 or MME2) to which the base station 2is connected to find core network entity 1 (such as AMF1 or MME1) towhich the base station 1 is connected. The base station 1 and the basestation 2 may also be connected to the same core network entity. Thatis, the core network entity 1 and the core network entity 2 may be thesame entity or different entities. The details are as described in theembodiments in FIGS. 6 and 7 .

The base station 2 does not need to decode the RLF report container ofthe base station 1. This method may simplify the base station 2.

If the base station 1 is the LTE base station ng-eNB or eNB, and thebase station 2 is the NR the base station gNB, the gNB does not need todecode the content of the UE RLF report, and knows the cell that lastserves the UE prior to the failure directly according to the cellidentity of the cell that last serves the UE before the failure occursincluded in the NR RRC message, and thus knows the base station whichcontrols the cell, and transmits a failure indication message to thebase station. The gNB may transmit a failure indication message to thebase station which controls the cell that last serves the UE prior tothe failure, without a support for implementing the RRC of the LTE.Similarly, in the case where there is no Xn interface between the basestation 1 and the base station 2, the gNB does not need to decode thecontent of the LTE RLF report, and may know the TAI of the cell wherethe failure occurs directly from the NR RRC message, so as to transmitthe RLF report to the base station 1 through the core network.Meanwhile, the UE does not need to wait to transmit the UE RLF reportuntil the UE reconnects to the LTE base station, which reduces the timefor the UE to store the RLF report and stores the UE's memory space.Similarly, in the case where there is no Xn interface between the basestation 1 and the base station 2, the gNB does not need to decode thecontent of the UE RLF report, and may know the TAI of the cell where thefailure occurs directly from the NR RRC message, so as to transmit theRLF report to the base station 1 through the core network.

If the base station 1 is the NR base station gNB, and the base station 2is the LTE base station ng-eNB or eNB, the ng-eNB or the eNB does notneed to decode the content of the NR RLF report, and knows the cell thatlast serves the UE prior to the failure directly according to the cellidentity of the cell that last serves the UE before the failure occursincluded in the LTE RRC message, and thus knows the base station whichcontrols the cell, and transmits a failure indication message to thebase station. The ng-eNB or the eNB may transmit a failure indicationmessage to the base station which controls the cell that last serves theUE prior to the failure, without a support for implementing the RRC ofthe NR. Similarly, in the case where there is no Xn interface betweenthe base station 1 and the base station 2, the ng-eNB or the eNB doesnot need to decode the content of the NR RLF report, and may know theTAI of the cell in which the failure occurs directly from the LTE RRCmessage, so as to transmit an RLF report to the base station 1 throughthe core network. Meanwhile, the UE does not need to wait to transmitthe UE RLF report until the UE re-connects to the NR base station, whichreduces the time for the UE to store the RLF report and stores the UE'smemory space.

Step 305: The base station 1 detects the cause of the failure occurring,such as too early handover, too late handover, or handover to wrongcell. The base station 1 may detect the cause of the failure occurringaccording to the existing mechanism, and details are not describedherein repeatedly.

For the too early handover or the handover to wrong cell, the basestation 1 transmits a handover report message to the base station whichcontrols the source cell that triggers the last handover, such as thebase station 3. The base station 1 knows the identity of the source cellthat triggers the last handover according to the UE RLF report. Thehandover report message includes the cell identity of the cell where theUE attempts to establish the RRC connection, or the UE establishes theRRC connection, after the failure. Optionally, the handover reportmessage may include the cell identity of the target cell for thehandover. If the base station 1 and the base station 3 belong to basestations supporting different radio access technologies, the handoverreport may not include the UE RLF report. The handover report messagedirectly includes a combination of one or more of the followinginformation:

-   -   Time elapsed from the beginning of the last handover to the        failure;    -   Connection failure being an RLF or a handover failure;    -   Radio measurements of the UE;    -   C-RNTI allocated to the UE in the cell that last serves the UE        prior to the failure;    -   Cause of triggering an RLF;    -   Cell identity of the cell where the UE attempts to re-establish        the RRC connection, or the UE attempts to establish the RRC        connection, or the UE establishes the RRC connection, after the        failure;    -   Time elapsed from the failure to the UE RLF report;    -   Beam measurements of serving cell and neighboring cells,        especially beam measurements related to the SSB/CSI-RS;    -   Uncompensated barometric measurement;    -   Information on speed and direction of the UE.

The base station 1 obtains the above information from the UE RLF report,and the base station 1 makes one or more of the above informationincluded directly in the handover report message and sends the handoverreport message to the base station 3. The base station 1 may makes oneor more of the above information included in the handover report messagein the case where the base station 3 and the base station 1 supportdifferent radio access technologies. The meaning of the base station 1making one or more of the above information included directly in thehandover report message refers to including one or more of the aboveinformation in the application protocol message of Xn or X2 or NG or S1or other network interface, rather than including one or more of theabove information in the UE RLF report, comprised in the networkinterface message, and its meaning applies as well in the followingdescription.

In this way, the base station 3 may know more information about thefailure without parsing the RRC information of other radio accesstechnologies, i.e., without parsing the content in the RLF report ofdifferent radio access technologies, so as to confirm the cause of thefailure and make reasonable parameter adjustments to avoid futurefailures.

So far, the description of the first method for supportingself-configuration and self-optimization of the present disclosure iscompleted. This method may enable the network to correctly detect thecause of the failure in the case that the UE fails when moving betweendifferent RATs, while reducing the time for the UE to store RLF reportinformation and reducing the process on the base station side, that isto say, the NR base station does not need to decode the content of theLTE, RRC and the LTE base station does not need to decode the content ofthe NR RRC.

A second method for supporting self-configuration and self-optimizationaccording to the present disclosure is illustrated as FIG. 4 . Adetailed description of steps which are not related to the presentdisclosure is omitted here. In the method, base station 1 and basestation 2 may be base stations of different radio access technologies,for example, the base station 1 is an ng-eNB or an eNB that supports anUE air interface technology, and the base station 2 is a gNB thatsupports the NR radio access technology. Alternatively, the base station1 is a gNB that supports the NR radio access technology, and the basestation 2 is an ng-eNB or an eNB that supports the UE air interfacetechnology. The base station 3 may be a base station that supports anyradio access technology, for example, the same radio access technologyas that supported by the base station 1, the same radio accesstechnology as that supported by the base station 2, or other radioaccess technologies. The method includes steps as follows.

Step 401: A UE fails in a cell of the base station 1, and it is assumedthat the UE fails in the cell A. The failure here may be an RLF or ahandover failure. For the handover failure, the cell A is a target cellfor the handover. The cell where the failure occurs is also the cellthat last serves the UE prior to the failure. The UE stores one or moreof the following information:

-   -   Cell identity of the cell A, which may be a global cell identity        or a physical cell identifier (PCI) and frequency information;    -   Tracking area code (TAC) or tracking area identity (TAI) of the        cell A;    -   Cell identity of the source cell that triggers the last        handover;    -   TAC or TAI of the source cell that triggers the last handover;    -   Time elapsed from the beginning of the last handover to the        failure;    -   Connection failure being an RLF or a handover failure;    -   Radio measurements of the UE;    -   C-RNTI allocated to the UE by the cell that last serves the UE        prior to the failure;    -   Cause of triggering an RLF;    -   Cell identity of the cell where the UE attempts to re-establish        the RRC connection, or the UE attempts to establish the RRC        connection, or the UE establishes the RRC connection, after the        failure;    -   Time elapsed from the failure to the UE RLF report.

The last two items may be stored in a subsequent procedure. For example,when the UE attempts to re-establish the RRC connection, the UE recordsthe cell identity of the cell where the UE attempts to re-establish theRRC connection after the failure. When the UE prepares to transmit theRLF report, the UE records the time elapsed from the failure to the UERLF report.

All the above cell identities may be the global cell identity or the PCIand the frequency information.

The UE also stores the RLF report of which radio access technology thestored RLF report information is, such as an UE RLF report or an NR RLFreport.

If the base station 1 is the LTE base station (for example, an ng-eNB oran eNB), the above RLF report information is the LTE RLF report, whichis in the format and encoding of the LTE RRC.

If the base station 1 is an NR base station (for example, a gNB), theabove-mentioned RLF report information is the NR RLF report, which is inthe format and encoding of the NR RRC.

Step 402: The UE re-establishes the RRC connection in a cell of the basestation 2. The UE may re-establish the RRC connection through the RRCconnection establishment or RRC connection re-establishment procedure.In the RRC connection establishment completion or RRC connectionre-establishment completion message, the UE indicates, to the network,that the RLF report information is available. The UE may indicate, tothe network, that the RLF report information is available. The UE mayalso indicate, to the network, that the RLF report information of whichradio access technology is available, for example, the UE indicates, tothe network, that the LTE RLF report or the NR RLF report is available.The UE may also indicate, to the network, the LTE RLF report and the NRRLF report are available.

The method of the present disclosure may further include the step of:broadcasting, by the base station, whether the base station supports theRLF information reporting, or broadcasting, by the base station, the RFLinformation reporting of which radio access technology the base stationsupports. For example, the LTE base station broadcasts whether the LTEbase station supports the NR RLF information reporting and/or the LTERLF information reporting, and the NR base station broadcasts whetherthe NR base station supports the LTE RLF information reporting and/orthe NR RLF information reporting. If the base station with which the UEre-establishes the RRC connection supports the RLF informationreporting, or supports the RLF information reporting of thecorresponding radio access technology stored by the UE, the UEtransmits, to the re-accessed base station, that the RLF informationreporting or the RLF information reporting of which radio accesstechnology is available. For example, the UE may indicate to the basestation that the RLF information reporting to the base station isavailable, and the UE may also indicate that the NR RLF informationreporting or the LTE RLF information reporting to the base station isavailable.

If the base station 2 is the NR base station gNB, and the UE stores theLTE RLF report, the UE indicates, to the base station 2, that the RLFreport information is available, through the RRC connectionestablishment completion or RRC connection re-establishment completionmessage of the NR. The UE may indicate that the RLF report informationis available to the base station 2 through the RRC connectionestablishment completion or RRC connection re-establishment completionmessage of the NR. The UE may also indicate, to the base station 2, theRLF report information of which radio access technology is available,for example, the UE indicates, to the base station 2, that the LTE RLFreport or the NR RLF report is available. The UE may also indicate, tothe base station 2, that the LTE RLF report and the NR RLF report areavailable.

If the base station 2 is the LTE base station ng-eNB or eNB, and the UEstores the NR RLF report, the UE indicates, to the base station 2, thatthe RLF report information is available, through the RRC connectionestablishment completion or RRC connection re-establishment completionmessage of the LTE. The UE may indicate that the RLF report informationis available to the base station 2 through the RRC connectionestablishment completion or RRC connection re-establishment completionmessage of the LTE. The UE may also indicate, to the base station 2, theRLF report information of which radio access technology is available,for example, the UE indicates, to the base station 2, that the LTE RLFreport or the NR RLF report is available. The UE may also indicate, tothe base station 2, that the LTE RLF report and the NR RLF report areavailable.

Step 403: The base station 2 requests the VIE to report the RLF report,and the UE transmits the UE RLF report to the base station 2.

The base station 2 may also indicate, to the UE, the RLF report of whichradio access technology is requested. For example, the base station 2requests the UE to report the LTE RLF report or the NR RLF report. Thebase station 2 may also request the UE to report the UE RLF report andthe NR RLF report. The base station 2 requests the UE to report the RLFreport according to the RLF report being available or the RFL report ofwhich radio access technology being available indicated by the UE in theRRC connection establishment completion or RRC connectionre-establishment completion message. For example, if the UE indicatesthat the LTE RLF report is available, and the base station 2 supportsthe request for the LTE report, the base station 2 may request the UE toreport the UE RLF report. If the UE indicates that the NR RLF report isavailable, and the base station 2 supports the request for the NRreport, the base station 2 may request the UE to report the NR RLFreport.

Alternatively, the base station does not need to distinguish between theradio access technologies. The UE indicates that the RLF report isavailable, and then the base station requests the UE to report the RLFreport.

The base station may request the UE RFL report through a UE informationrequest message. The UE information request may include the RLF reportof which radio access technology is requested, for example, the NR RLFreport is requested or the LTE RLF report is requested.

The UE may transmit the RFL report to the base station through a UEinformation response message. The UE information response messageincludes the RLF report. The RLF report may be the UTE RLF report and/orthe NR RLF report.

The UE RLF report includes the content described in step 401, the cellidentity of the cell that last serves the UE before the failure occursis included in the UE RLF report by the UE. The cell that last servesthe UE prior to the failure is also the cell where the failure occurs.For the handover failure, the cell is a target cell on a target basestation. All the cell identities may be the global cell identity or thePCI and frequency information. In the present embodiment, the cell iscell A.

The TAC or TAI of the cell that last serves the UE before the failureoccurs is included in the UE RLF report by the UE. The cell that lastserves the UE prior to the failure is also the cell where the failureoccurs. For handover failure, the cell is the target cell on the targetbase station. In the present embodiment, the cell is cell A.

If the base station 1 is the LTE base station and the base station 2 isthe NR base station, the LTE RLF report information is included in theNR RRC message by the UE.

If the base station 1 is the NR base station and the base station 2 isthe LTE base station, the NR RLF report information is included in theLTE RRC message by the UE.

Step 404: The base station 2 decodes the UE RLF report. The base station2 knows the cell that last serves the LTE prior to the failure accordingto cell identity of the cell that last serves the UE before the failureoccurs included in the RLF report included in the RRC message. Here, thecell that last serves the UE prior to the failure is controlled by thebase station 1. The base station 2 transmits a failure indicationmessage to the base station 1. The failure indication message includesthe RLF report received from the UE.

if there is no Xn interface between the base station 2 and the basestation 1, the base station 2 needs to transmit the failure indicationmessage to the base station 1 through the core network. The base station2 knows the TAI of the cell of the base station 1 from the cell identityof the cell that last serves the UE before the failure occurs and theTAC or TAI of the cell included in the RLF report included in the RRCmessage. The base station 2 transmits a message to the core network, andthe message includes the UE RLF report and the TAI of the cell in whichthe failure occurs. The TAI is used for routing in the core network, forexample, the TAI is used by core network entity 2 (such as AMF2 or MME2)to which the base station 2 is connected to find core network entity 1(such as AMF1 or MME1) to which the base station 1 is connected. Thebase station 1 and the base station 2 may also be connected to the samecore network entity. That is, the core network entity 1 and the corenetwork entity 2 may be the same entity or different entities. Thedetails are as described in the embodiments in FIGS. 6 and 7 .

The base station 2 needs to decode the RLF report container from thebase station 1.

If the base station 1 is the LTE base station ng-eNB, and the basestation 2 is the NR base station gNB, the gNB needs to decode thecontent of the LTE RLF report, and knows the cell that last serves theUE prior to the failure according to the cell identity of the cell thatlast serves the UE before the failure occurs included in the UE RLFreport, and thus knows the base station which controls the cell, andtransmits a failure indication message to the base station. The gNBneeds to support the RRC of the LTE so as to transmit a failureindication message to the base station which controls the cell that lastserves the UE prior to the failure. Similarly, in the case where thereis no Xn interface between the base station 1 and the base station 2,the gNB needs to decode the TAC or TAI included in the LTE RLF report,and knows the TAI of the cell in which the failure occurs, so as totransmit the RLF report to the base station 1 through the core network.This method has advantages in that the UE does not need to wait totransmit the LTE RLF report until the UE reconnects to the LTE basestation, which reduces the time for the UE to store the RLF report andstores the UE's memory space:

If the base station 1 is the NR base station gNB, and the base station 2is the LTE base station ng-eNB or eNB, the ng-eNB or the eNB needs todecode the content of the NR RLF report, and knows the cell that lastserves the UE prior to the failure according to the cell identity of thecell that last serves the UE before the failure occurs included in theNa RLF report, and thus knows the base station which controls the cell,and transmits a failure indication message to the base station. Theng-eNB or the eNB needs to support the RRC of the NR so as to transmit afailure indication message to the base station which controls the cellthat last serves the UE prior to the failure. Similarly, in the casewhere there is no Xn interface between the base station 1 and the basestation 2, the ng-eNB or the eNB needs to decode the content of the NRRLF report, and knows, from the NR RLF, the TAI of the cell where thefailure occurs, so as to transmit an RLF report to the base station 1through the core network. This method has advantages in that the UE doesnot need to wait to transmit the UE RLF report until the UE re-connectsto the NR base station, which reduces the time for the HE to store theRLF report and stores the UE's memory space.

Step 405: The base station 1 checks the cause of the failure occurring,such as too early handover, too late handover, or handover to wrongcell. The base station 1 may detect the cause of the failure occurringaccording to the existing mechanism, and details are not describedherein repeatedly.

For the too early handover or the handover to wrong cell, the basestation 1 transmits a handover report message to the base station whichcontrols the source cell that triggers the last handover, such as thebase station 3. The base station 1 knows the identity of the source cellthat triggers the last handover according to the UE RLF report. Thehandover report message includes the cell identity of the cell where theUE attempts to establish the RRC connection, or the UE establishes theRRC connection, after the failure. If the base station 1 and the basestation 3 belong to base stations supporting different radio accesstechnologies, the handover report may not include the UE RLF report. Thehandover report message directly includes a combination of one or moreof information as described in step 305, in this way, the base station 3may know more information about the failure without parsing the RRCinformation of other radio access technologies, so as to confirm thecause of the failure and make reasonable parameter adjustments to avoidfuture failures.

So far, the description of the second method for supportingself-configuration and self optimization of the present disclosure iscompleted. This method may enable the network to correctly detect thecause of the failure in the case that the UE fails when moving betweendifferent RATs, while reducing the time for the UE to store RLF reportinformation.

A third method for supporting self-configuration and self-optimizationaccording to the present disclosure is illustrated in FIG. 5 . Adetailed description of steps which are not related to the presentdisclosure is omitted here. This method is illustrated by taking anexample in which the failure occurs in an NR base station gNB, and thebase station that the UE re-accesses after the failure is an LTE basestation ng-eNB or eNB. Conversely, this method may be applicable aswell, for example, the failure occurs in the LTE base station ng-eNB oreNB, and the base station that the UE re-accesses after the failure isthe NR base station gNB.

The method includes steps as follows.

Step 501: A UE fails in a cell of the gNB1, and it is assumed that theVIE fails in cell A. Herein, the failure may be an RLF or a handoverfailure. For the handover failure, the cell A is a target cell for thehandover. The cell where the failure occurs is also the cell that lastserves the UE prior to the failure. The UE stores one or more of thefollowing information:

-   -   Cell identity of the cell A, which may be a global cell identity        or a physical cell identifier (PCI) and frequency information;    -   Tracking area code (TAC) or tracking area identity (TAI) of the        cell A;    -   Cell identity of the source cell that triggers the last        handover;    -   Time elapsed from the beginning of the last handover to the        failure;    -   Connection failure being an RLF or a handover failure;    -   Radio measurements of the UE;    -   C-RNTI allocated to the UE by the cell that last serves the UE        prior to the failure;    -   Cause of triggering an RLF;    -   Cell identity of the cell where the UE attempts to re-establish        the RRC connection after the failure;    -   Cell identity of the cell where the UE successfully establishes        the RRC connection, or cell identity of the cell where the UE        attempts to establish the PAC connection, after the failure;    -   Time elapsed from the failure to the UE RLF report.    -   Time elapsed from the failure to the RRC re-connection attempt        or successful access to the network. The RRC re-connection        attempt refers to transmission of an RRC connection        establishment request or RRC connection re-establishment request        message. The successful access to the network may be that the UE        transmits the RRC connection establishment completion or RRC        connection re-establishment completion or RACH success message.

The last four items may be stored in a subsequent procedure. Forexample, when the UE attempts to re-establish the RRC connection, the UErecords the cell identity of the cell where the UE attempts tore-establish the RRC connection after the failure. When the UEsuccessfully re-establishes the RRC connection or the LT attempts toestablish the RRC connection, the LT records the cell identity of thecell where the UE successfully establishes the RRC connection or thecell identity of the cell where the UE attempts to establish the RRCconnection. When the UE prepares to transmit the RLF report, the UErecords the time elapsed from the failure to the UE RLF report. Uponsuccessful access to the network, the UE records the time elapsed fromthe failure to successful access to the network.

All the above cell identities may be the global cell identity or the PCIand the frequency information.

The LTE also stores the RLF report of which radio access technology thestored RLF report information is, such as an LTE RLF report or an NR RLFreport.

The above-mentioned RLF report information is an NR RLF report, which isin a format and encoding of the NR RRC.

Step 502: The UE re-establishes the RRC connection in the cell of theng-eNB1 or the eNB. The UE may re-establish the RRC connection throughthe RRC connection establishment or RRC connection re-establishmentprocedure. In the RRC connection establishment completion or RRCconnection re-establishment completion message, the UE indicates, to thenetwork, that the RLF report information is available. Step 503: the UEis connected to the gNB2. The LTE may access the gNB2 through RRCconnection establishment or RRC connection re-establishment or handover.In the RRC connection establishment completion or RRC connectionre-establishment completion or RRC reconfiguration completion message,the UE indicates, to the network, that the RLF report information isavailable. The RRC reconfiguration completion message is used toindicate the handover completion. The UE may also indicate, to thenetwork, that the RLF report information of which radio accesstechnology is available, for example, in the present embodiment, the UEindicates, to the network, that the NR RLF report is available.

The method of the present disclosure may further include the step ofbroadcasting, by the base station, whether the base station supports theRFL information reporting. If the base station with which the UEre-establishes the RRC connection supports the RLF informationreporting, the UE transmits, to the re-accessed base station, that theRLF information reporting is available. For example, the UE mayindicate, to the base station, that the RLF information reporting isavailable.

The UE stores that the RLF report information is the report of whichradio access technology, and when the UE re-accesses the base station ofthe corresponding radio access technology, the UE indicates, to the basestation, that the RLF report information is available.

The gNB2 requests the UE to report the RLF report, and the UE transmitsa UE RLF report to the gNB2.

The UE RLF report includes the content described in step 501. The gNB2knows the base station which controls the cell where the failure occurs,according to the cell identity of the cell that last serves the UEbefore the failure occurs included in the UE RLF report. The gNB2transmits a failure indication message to the gNB1. The failureindication message includes the RLF report received from the UE.

If there is no Xn interface between the gNB2 and the gNB1, the gNB2needs to transmit the RLF report to the gNB1 through the core network.The gNB2 knows the TAI of the cell where the failure occurs from thecell identity of and the TAC or TAI of the cell where the failure occursincluded in the LTE RLF report. The gNB2 transmits the RLF reportreceived from the LTE through the NG interface, the transmitted RIXreport message includes the TAI of the cell where the failure occurs.The TAI is used for routing in the core network, for example, the TAI isused by core network entity 2 (such as AMF2) to which the gNB2 isconnected to find core network entity 1 (such as AMF1) to which the gNB1is connected. The gNB1 and the gNB2 may also be connected to the sameAMF. That is, the AMF1 and the AMF2 may be the same AMF or differentAMFs. The details are as described in the embodiments in FIGS. 6 and 7 .

Step 504: The gNB2 transmits a failure indication message to the gNB1.The failure indication message includes the RLF report received from theUE.

If there is no Xn interface between the gNB 2 and the gNB1, the gNB 2needs to transmit a failure indication message to the gNB 1 through thecore network. The gNB 2 knows the TAI of the cell of the base station 1,from the cell identity of the cell that last serves the UE before thefailure occurs and the TAC or TAI of the cell included in the RFL reportincluded in the RRC message. The gNB 2 transmits a message to the corenetwork, and the message includes the UE RFL report and the TAI of thecell in which the failure occurs. The TAI is used for routing in thecore network, for example, the TAI is used by core network entity 2(such as AMF2) to which the gNB2 is connected to find the core networkentity 1 (such as AMF1) to which the gNB1. is connected. The gNB1 andthe gNB2 may also be connected to the same AMF, that is, AMF1 and AMF2may be the same AMF or different AMFs. The details are as described inthe embodiments in FIGS. 6 and 7 .

Step 505: The gNB1 checks the cause of the failure occurring, such astoo early handover, too late handover, or handover to wrong cell. ThegNB1 knows the right cell to which the UE may be handed over accordingto the cell identity of cell where the UE successfully establishes theRRC connection or the cell identity of cell where the UE attempts toestablish the RRC connection, after the failure. For the too latehandover, the failed cell may handover the UE to the cell where the UEsuccessfully establishes the RRC connection or the cell where the UEattempts to establish the RRC connection. For the too early handover orthe handover to wrong cell, the source cell that triggers the lasthandover may handover the UE to the cell where the UE successfullyestablishes the RRC connection or the cell where the UE attempts toestablish the RRC connection. The gNB1 may also determine whether thecell where the UE successfully establishes the RRC connection or thecell where the UE attempts to establish the RRC connection after thefailure is a suitable handover cell according to the time elapsed fromthe failure to the successful access to the network or the time elapsedfrom the failure to the RRC re-connection attempt.

For the too early handover or the handover to wrong cell, the gNB1transmits a handover report message to the base station which controlsthe source cell that triggers the last handover, such as the eNB or theng-eNB or the gNB. The gNB1 knows the identity of the source cell thattriggers the last handover according to the UE RLF report. The handoverreport message includes the cell identity of the cell where the UEattempts to establish the RRC connection or the cell identity of thecell the UE establishes the RRC connection, after the failure.Optionally, the handover report message may include the cell identity ofthe target cell for the handover. If the base station that triggers thelast handover is not a base station that supports the NR accesstechnology (for example, the eNB or the ng-eNB), the handover report maynot include the UE RLF report. The handover report message directlyincludes a combination of one or more of the information described instep 305, in this way the eNB or the ng-eNB may know more informationabout the failure without parsing the NR RRC information, so as toconfirm the cause of the failure and make reasonable parameteradjustments to avoid future failures. The gNB1 obtains the one or moreinformation described in step 305 from the UE RLF report, and the gNB1makes one or more of the information directly included in the handoverreport message, and sends the handover report message to the basestation which controls the source cell that triggers the last handover.The gNB1 may makes one or more of the above information included in thehandover report message in the case where the base station that triggersthe last handover is not a base station that supports the NR radioaccess technology. In this way, the base station that triggers the lasthandover may determine the cause of the failure and make reasonableparameter adjustments to avoid future failure, without parsing thecontent in the UE RLF report of different radio access technologies.

So far, the description of the third method for supportingself-configuration and self-optimization of the present disclosure iscompleted. This method may enable the network to correctly detect thecause of the failure in the case that the UE fails when moving betweendifferent RATs, while reducing the process on the base station side,that is, the NR base station does not need to decode the content of theLTE RRC and the LTE base station does not need to decode the content ofthe NR RRC.

A first embodiment of the first method for supporting self-configurationand self-optimization according to the present disclosure is illustratedin FIG. 6 . A detailed description of steps which are not related to thepresent disclosure is omitted here. The method includes steps asfollows.

Step 601: A UE fails in a cell of an ng-eNB1 or an eNB, and it isassumed that the UE fails in cell A. The failure here may be an RLF or ahandover failure, For the handover failure, the cell A is a target cellfor the handover. The cell where the failure occurs is also the cellthat last serves the UE prior to the failure. The UE stores one or moreof the following information:

-   -   Cell identity of the cell A, which may be a global cell identity        or a physical cell identifier (PCI) and frequency information;    -   Tracking area code (TAC) or tracking area identity (TAI) of the        cell A;    -   Cell identity of the source cell that triggers the last        handover;    -   TAC or TAI of the source cell that triggers the last handover;    -   Time elapsed from the beginning of the last handover to the        failure;    -   Connection failure being an RLF or a handover failure;    -   Radio measurements of the UE;    -   C-RNTI allocated to the UE by the cell that last serves the UE        prior to the failure;    -   Cause of triggering an RLF;    -   Cell identity of the cell where the UE attempts to re-establish        the RRC connection, or cell identity of the cell where the UE        attempts to establish the RRC connection, or cell identity of        the cell where the LTE establishes the RRC connection, after the        failure;    -   Time elapsed from the failure to the UE RLF report.

The last two items may be stored in a subsequent procedure. For example,when the LTE attempts to re-establish the RRC connection, the UE recordsthe cell identity of the cell where the UE attempts to re-establish theRRC connection after the failure. When the UE prepares to transmit theRLF report, the UE records the time elapsed from the failure to the UERLF report.

All the above cell identities may be the global cell identity or the PCIand the frequency information.

The LTE also stores the RLF report of which radio access technology thestored RLF report information is, for example, the stored RLF reportinformation is an LTE RLF report in the present embodiment.

The above RLF report information is the UE RLF report, which is in theformat and encoding of the LTE RRC.

Step 602: The UE re-establishes the RRC connection in a cell of thegNB1. The UE may re-establish the RRC connection through the RRCconnection establishment or RRC connection re-establishment procedure.In the RRC connection establishment completion or RRC connectionre-establishment completion message, the UE indicates, to the network,that the RLF report information is available. The UE may indicate, tothe network, that the RLF report information is available. The UE mayalso indicate, to the network, that the RLF report information of whichradio access technology is available, for example, the UE indicates tothe network the LTE RLF report is available in the present embodiment.

Through the RRC connection establishment completion or RRC connectionre-establishment completion message of the NR, the UE indicates, to thegNB1, that the RLF report or the LTE RLF report information isavailable. The RLF report is the LTE RLF report.

The method of the present disclosure may further include the step of:broadcasting, by the base station, whether the base station supports theRLF information reporting, or broadcasting, by the base station, the RLFinformation reporting of which radio access technology the base stationsupports. For example, the gNB1 broadcasts whether the gNB1 supports theLTE RLF information reporting and/or the NR RLF information reporting.If the gNB1 supports the RLF information reporting, or the RLFinformation reporting of the corresponding radio access technologystored by the UE, the UE transmits, to the re-accessed gNB1, the RLFinformation reporting or the RLF information reporting of thecorresponding radio access technology is available. For example, thegNB1 broadcasts that the gNB1 supports the UE RLF information reporting,and the UE stores the UE RLF report, thus the UE may indicate to thegNB1 that the LTE RLF reporting to the gNB1 is available.

Step 603: The gNB1 requests the UE to report the RLF report, and the UEtransmits the UE RLF report to the gNB1

The gNB1 requests the UE to report the RLF report according to the RLFreport being available indicated by the UE in the RRC connectionestablishment completion or RRC connection re-establishment completionmessage.

The gNB1 may also indicate, to the UE, the LTE RLF report is requested.The gNB1 requests the UE to report the LTE RLF report according to theRLF report being available indicated by the UE in the RRC connectionestablishment completion or RRC connection re-establishment completionmessage. For example, if the UE indicates the UE RLF report isavailable, and the gNB1 supports the request for the LTE RLF report thegNB1 may request the UE to report the LTE RLF report.

Alternatively, the base station does not need to distinguish between theradio access technologies. The UE indicates that the report isavailable, and then the base station requests the UE to report the RLFreport.

The base station may request the LTE, RLF report through a UEinformation request message. The UE information request may include theRFL report of which radio access technology is requested, for example,the NR RLF report is requested or the LTE RLF report is requested.

The UE may transmit the RLF report to the base station through a UEinformation response message. The FIE information response messageincludes the RLF report. The RLF report may be the LTE RFL report and/orthe NR RLF report.

The UE RLF report includes the content described in step 601. In the UERLF report, the cell identity of the cell that last serves the UE beforethe failure occurs is included. In the message of transmitting the UERLF report (outside the UE RLF report container), the cell identity ofthe cell that last serves the UE before the failure occurs is alsoincluded. The cell that last serves the UE prior to the failure is alsothe cell where the failure occurs. For the handover failure, the cell isa target cell of a target base station. All the cell identities may bethe global cell identity or the PCI and frequency information. In thepresent embodiment, the cell is cell A.

In the UE RLF report, the TAC or TAI of the cell that last serves the UEbefore the failure occurs is included. In the NR RRC message oftransmitting the UE RLF report (outside the UE RLF report container),the TAC or TAI of the cell that last serves the UE before the failureoccurs is also included. The cell that last serves the UE prior to thefailure is also the cell where the failure occurs. For handover failure,the cell is the target cell of the target base station. In the presentembodiment, this cell is cell A.

The LTE RLF report information is included in the NR RRC message by theUE, and cell identity of the cell that last serves the UE before thefailure occurs and/or the TAC or TAI of the cell are also included inthe NR RRC message (outside the LTE RLF report container) by the UE.

Step 604: The gNB1 knows the cell that last serves the UE prior to thefailure according to the cell identity of the cell that last serves theUE before the failure occurs included in the NR RRC message, and thusknows the base station which controls this cell. Here, the cell thatlast serves the LTE prior to the failure is controlled by the ng-eNB1 oreNB1.

If there is no Xn interface between the gNB1 and the ng-eNB1 or there isno interface between the gNB1 and the eNB1, the gNB1 needs to transmitthe RLF report received from the UE to the ng-eNB1 or the eNB1 throughthe core network. Therefore, the UE RLF report information is includedin the inter-system self-optimization (SON) message at an interfacebetween the gNB and the 5GS and an interface between the eNB to the EPC.

The gNB1 transmits an uplink RAN configuration transfer of an NGapplication protocol (AP) message to the AMF. Here, other NGAP messagesare possible to be used. The message includes the TAI of the cell inwhich the failure occurs and/or the base station identity of the basestation which controls the cell in which the failure occurs. The gNB1sets the identity of the target base station in the message as the basestation identity of the base station which controls the cell where thefailure occurs. The gNB1 knows the TAI of the cell in which the failureoccurs according to the cell identity and the TAC or TAI of the cellwhere the failure occurs received from the NR RRC message. The gNB1knows the base station identity of the base station which controls thecell where the failure occurs according to the cell identity of the cellwhere the failure occurs received from the NR RRC message, that is, thebase station identity of the ng-eNB1 or the eNB1.

The TAI is used for routing in the core network. For example, the AMFentity to which the gNB1 is connected uses the TAI to find the AMFentity to which the ng-eNB1 is connected or the MME entity to which theeNB is connected, and forwards the information in the uplink accessconfiguration transmission message to the AMF to which the ng-eNB1 isconnected or the MME entity to which the eNB is connected. The NB1 andng-eNB1 may be connected to the same AMF or different AMFs, and the AMFentity to which the gNB1 is connected knows whether the gNB1 and ng-eNBare connected to the same AMF, according to the TAI.

In an actual network, the UE base station where the UE fails may be anng-eNB connected to the 5GC or an eNB connected to the MME. When thefailure occurs at the eNB, the content of the UE RLF is the same as thatwhen the failure occurs at the ng-eNB. If the failure occurs at theng-eNB, the TAC of the cell in which the failure occurs is 3 bytes inlength, and if the failure occurs at the eNB, the TAC of the cell inwhich the failure occurs is 2 bytes in length. The AMF can know whetherthe cell where the failure occurs is controlled by an eNB or an ng-eNBbased on the length of the TAC. If the failure occurs is controlled bythe eNB, the AMF finds the MME connected to the base station whichcontrols the cell where the failure occurs according to the TAI, and theAMF transmits the information of the NGAP message received from the gNBto the MME. The MME transmits a UE RLF report to the eNB which controlsthe cell where the failure occurs, according to the target base stationidentity.

The identity of the base station which controls the cell where thefailure occurs is used by the core network to transmit a downlink RANconfiguration transfer message to the ng-eNB1, otherwise the AMF doesnot know to which base station the message may be transmitted.

The gNB1 does not need to decode the RLF report container of the LTE.This method may simplify the base station.

The gNB1 knows the cell that last serves the UI prior to the failuredirectly according to the cell identity of the cell that last serves theUE before the failure occurs included in the NR RRC message, and thusknows the base station which controls the cell, and transmits a failureindication message to the base station. The gNB1 may transmit a failureindication message to the base station which controls the cell that lastserves the UE prior to the failure, without a support for implementingthe RRC of the LTE. Similarly, in the case where there is no Xninterface between the gNB1 and the ng-eNB1, the gNB1 does not need todecode the content of the LTE RLF report, and may know the TAI of thecell where the failure occurs directly from the NR RRC message, and knowthe base station identity of the base station which controls the cellwhere the failure occurs according to the cell identity of the cellwhere the failure occurs, so as to transmit the RLF report to theng-eNB1 through the core network. Meanwhile, the UE does not need towait to transmit the UE RLF report until the UE reconnects to the LTEbase station, which reduces the time for the UE to store the RLF reportand stores the UE's memory space. Similarly, in the case where there isno Xn interface between the gNB1 and the ng-eNB1, the gNB1 does not needto decode the content of the LTE RLF report, and may know the TAI of thecell where the failure occurs and/or the base station identity of thebase station which controls the cell where the failure occurs directlyfrom the NR RRC message, so as to transmit the RLF report to the ng-eNB1through the core network.

Step 605: The AMF transmits a downlink RAN configuration transfer of theNGAP message to the ng-eNB1 Here, other NGAP messages are possible to beused. The AMF knows which base station the message is to be transmittedto, according to the identity of the target base station. For the casewhere the base station where the UE fails is an eNB1, the MME transmitsan MME configuration transfer of the S1AP message to the eNB1. Here,other S1AP messages are possible to be used. The MME knows which basestation the message is to be transmitted to, according to the identityof the target base station.

Step 606: The ng-eNB1 or the eNB detects the cause of the failureoccurring, such as too early handover, too late handover, or handover towrong cell. The ng-eNB1 or the eNB may detect the cause of the failureoccurring according to the existing mechanism, and details are notdescribed herein repeatedly.

For too early handover or handover to wrong cell, the ng-eNB1 or the eNBtransmits a handover report message to the base station which controlsthe source cell that triggers the last handover, such as the ng-eNB1 orthe eNB or the gNB. The ng-eNB1 or the eNB knows the identity of thesource cell that triggers the last handover according to the UE RLFreport, and may thus know the base station identity of the base stationwhich controls the source cell that triggers the last handover. Thehandover report message includes the cell identity of the cell where theUE attempts to establish the RRC connection, or the cell identity of thecell where the UE establishes the RRC connection, after the failure.Optionally, the handover report message may include the cell identity ofthe target cell for the handover. If the base station that triggers thelast handover is not a base station supporting the LTE access technology(e.g., the gNB), the handover report may not include the UE RLF report.The handover report message directly includes a combination of one ormore of information as described in step 305. In this way, the gNB mayknow more information about the failure without parsing the LTE RRCinformation, so as to confirm the cause of the failure and makereasonable parameter adjustments to avoid future failures. The ng-eNB1or the eNB obtains the one or more information described in step 305from the UE RLF report, and the ng-eNB1 or the eNB makes one or more ofthe information directly included in the handover report message, andsends the handover report message to the base station which controls thesource cell that triggers the last handover. The ng-eNB1 or the eNB maymakes one or more of the above information included in the handoverreport message in the case where the base station that triggers the lasthandover is not a base station that supports the LTE radio accesstechnology. In this way, the base station that triggers the lasthandover may determine the cause of the failure and make reasonableparameter adjustments to avoid future failures, without parsing thecontent of the UE RLF report in different radio access technologies.

If there is no Xn interface between the ng-eNB1 or the eNB and the basestation which controls the source cell that triggers the last handover,the handover report needs to be transmitted through the core network tothe base station, the ng-eNB or the eNB or the gNB, which controls thesource cell that triggers the last handover.

The ng-eNB1 transmits an uplink RAN configuration transfer of the NGAPmessage to the ANTE The eNB transmits the eNB configuration transfermessage to the MMF. The TAI included in the message is set as the TAI ofthe source cell that triggers the last handover. The target base stationidentity is set as the base station identity of the base station whichcontrols the source cell that triggers the last handover. The messageincludes information about the too early handover or the handover towrong cell. The message may also be other NGAP or S1AP messages. Theng-eNB1 or the eNB knows the TAI of the source cell that triggers thelast handover according to the UE RLF report, and knows the base stationidentity of the base station which controls the source cell thattriggers the last handover according to the cell identity of the sourcecell that triggers the last handover.

Step 607: The AMF transmits a downlink RAN configuration transfer of theNGAP message to the ng-eNB or the gNB. For the case where the basestation that last triggers the handover is an LTE base station eNB, theMME transmits an MME configuration transfer of the S1AP message to theeNB. Here, other S1AP messages are possible to be used. The MME knowswhich base station the message is to be transmitted to, according to thetarget base station identity. The detailed description of the procedurebetween the AMF and the MME is omitted here.

So far, the description of the first embodiment of the first method forsupporting self-configuration and self-optimization of the presentdisclosure is completed. This method may enable the network to correctlydetect the cause of the failure in the case that the UE fails whenmoving between different RATs, while reducing the time for the UE tostore RLF report information and reducing the process on the basestation side, that is, the NR base station does not need to decode thecontent of the UE RRC and the LTE base station does not need to decodethe content of the NR RRC. When there is no Xn interface between thebase station which controls the cell where the failure occurs and thebase station which controls the cell where the UE reconnects, the NRbase station may still transmit the RLF report to the base station whichcontrols the cell where the failure occurs through the core networkwithout parsing the LTE RLF. When there is no Xn interface between thebase station which controls the cell where the failure occurs and thebase station which controls the cell that triggers the last handover,the base station which controls the cell where the failure occurs maystill transmit a handover report to the base station which controls thesource cell that triggers the last handover.

A second embodiment of the first method for supportingself-configuration and self-optimization according to the presentdisclosure is illustrated in FIG. 7 . A detailed description of stepswhich are not related to the present disclosure is omitted here. Themethod includes steps as follows.

Step 701: A UE fails in a cell of a gNB1, and it is assumed that the LTEfails in cell A.

The failure here may be an RLF or a handover failure. For handoverfailure, the cell A is a target cell for the handover. The cell wherethe failure occurs is also the cell that last serves the UE prior to thefailure. The UE stores one or more of the following information:

-   -   Cell identity of the cell A, which may be a global cell identity        or a physical cell identifier (PCI) and frequency information;

Tracking area code (TAC) or tracking area identity (TAI) of the cell A;

-   -   Cell identity of the source cell that triggers the last        handover;    -   TAC or TAI of the source cell that triggers the last handover;    -   Time elapsed from the beginning of the last handover to the        failure;    -   Connection failure being an RLF or a handover failure;    -   Radio measurements of the UE;    -   C-RNTI allocated to the UE by the cell that last serves the UE        prior to the failure;    -   Cause of triggering an RLF;    -   Cell identity of the cell where the LTE attempts to re-establish        the RRC connection, or cell identity of the cell where the UE        attempts to establish the RRC connection, or cell identity of        the cell where the UE establishes the RRC connection, after the        failure;    -   Time elapsed from the failure to the UE RLF report.

The last two items may be stored in a subsequent procedure, For example,when the UE, attempts to re-establish the RRC connection, the UE recordsthe cell identity of the cell where the UE attempts to re-establish theRRC connection after the failure. When the UE prepares to transmit theRLF report, the UE records the time elapsed from the failure to the UERLF report.

All the above cell identities may be the global cell identity or the PCIand the frequency information,

The UE also stores the RLF report of which radio access technology thestored RLF report information is, for example, the stored RLF reportinformation an NR RLF report in the present embodiment.

The above RLF report information is the NR RLF report, which is in theformat and encoding of the NR RRC.

Step 702: The UE re-establishes the RRC connection in a cell of theng-eNB1 or the eNB1. The UE may re-establish the RRC connection throughthe RRC connection establishment or RRC connection re-establishmentprocedure. In the RRC connection establishment completion or RRCconnection re-establishment completion message, the UE indicates, to thenetwork, that the RLF report information is available. The UE mayindicate, to the network, that the RLF report information is available.The UE may also indicate, to the network, that the RLF reportinformation of which radio access technology is available, for example,the UE indicates, to the network, that the NR report is available in thepresent embodiment.

Through the RRC connection establishment completion or RRC connectionre-establishment completion of the LTE RRC message, the UE indicates, tothe ng-eNB1 or the eNB1, the RLF report or the NR RLF report informationis available. The RLF report is the NR RLF report.

The method of the present disclosure may further include the step of:broadcasting, by the base station, whether the base station supports theRLF information reporting, or broadcasting, by the base station, the RLFinformation reporting of which radio access technology the base stationsupports. For example, the ng-eNB1 or the eNB1 broadcasts whether theng-eNB1 or the eNB1 supports the LTE RLF information reporting and/orthe NR RLF information reporting. If the ng-eNB1 or the eNB1 supportsthe RLF information reporting, or the RLF information reporting of thecorresponding radio access technology stored by the UE, the UEtransmits, to the re-accessed ng-eNB1 or eNB1, the RLF informationreporting or the RLF information reporting of the corresponding radioaccess technology is available. For example, the ng-eNB1 or the eNB1broadcasts that ng-eNB1 or the eNB1 supports the NR RLF informationreporting, and the UE stores the NR RLF report, thus the UE mayindicate, to the ng-eNB1 or the eNB1, the NR RLF information reportingis available.

Step 703: The ng-eNB1 or the eNB 1 requests the UE to report the RLFreport, and the UE transmits the UE RLF report to the ng-eNB1 or theeNB1.

The ng-eNB1 or the eNB1 requests the UE to report the RLF reportaccording to the RLF report being available indicated by the UE in theRRC connection establishment completion or RRC connectionre-establishment completion message.

The ng-eNB1 or the eNB1 may also indicate, to the UE, the NR RLF reportis requested. The ng-eNB1 or the eNB1 requests the UE to report the NRRLF report according to the NR RLF report being available indicated bythe UE in the RRC connection establishment completion or RRC connectionre-establishment completion message. For example, if the UE indicatesthe NR RLF report, and the ng-eNB1 or the eNB1 supports the request forthe NR RLF report, the ng-eNB1 or the eNB1 may request the UE to reportthe NR RLF report.

The base station may request the UE RLF report through UE informationrequest message. The UE information request may include the RLF reportof which radio access technology is requested, for example, the NR RLFreport is requested or the LTE RLF report is requested.

The UE may transmit the RLF report to the base station through a UEinformation response message. The UE information response messageincludes the RLF report. The RLF report may be the LTE RLF report and/orthe NR RLF report.

The UE RLF report includes the content described in step 701. For the inthe UE RLF report, the cell identity of the cell that last serves theLTE before the failure occurs is included. Meanwhile, in the UTE RRCmessage of transmitting the UE RLF report (outside the UE reportcontainer), the cell identity of the cell that last serves the UE beforethe failure occurs is also included. The cell that last serves the UEprior to the failure is also the cell where the failure occurs. For thehandover failure, the cell is a target cell of a target base station.All the cell identities may be the global cell identity or the PCI andfrequency information. In the present embodiment, the cell is cell A.

In the UE RLF report, the TAC or TAI of the cell that last serves the UEbefore the failure occurs is included. In the LTE RRC message oftransmitting the LTE RLF report (outside the UE RLF report container),the TAC or TA1 of the cell that last serves the UE before the failureoccurs is also included. The cell that last serves the UE prior to thefailure is also the cell where the failure occurs. For handover failure,the cell is the target cell of the target base station. In the presentembodiment, the cell is cell A.

The NR RFL report information is included in the LTE RRC message by theUE, and cell identity of the cell that last serves the UE before thefailure occurs and/or the TAC or TAI of the cell are also included inthe LTE RRC message (outside the NR RLF report container) by the UE.

Step 704: The ng-eNB1 or the eNB1 knows the cell that last serves the UEprior to the failure according to the cell identity of the cell thatlast serves the UE before the failure occurs included in the LTE RRCmessage, and thus knows the base station which controls this cell. Here,the cell that last serves the UE prior to the failure is controlled bythe gNB1.

If there is no Xn interface between the gNB1 and the ng-eNB1 or there isno interface between the gNB1 and the eNB1, the ng-eNB1 or the eNB1needs to transmit the RLF report received from the UE to the gNB1through the core network.

The ng-eNB1 transmits an uplink RAN configuration transfer of an NGApplication Protocol (AP) message to the AMF. Here, other NGAP messagesare possible to be used. The eNB1 transmits an eNB configurationtransfer of the S1AP message to the MME. Here, other S1AP messages arepossible to be used. The message includes the TAI of the cell in whichthe failure occurs and/or the base station identity of the base stationwhich controls the cell in which the failure occurs. The ng-eNB1 or theeNB1 sets the identity of the target base station in the message as thebase station identity of the base station which controls the cell wherethe failure occurs. The ng-eNB1 or the eNB1 knows the TAI of the cell inwhich the failure occurs according to the cell identity and the TAC orTAI of the cell where the failure occurs received from the LTE RRCmessage. The ng-eNB1 or the eNB1 knows the base station identity of thebase station which controls the cell where the failure occurs accordingto the cell identity of the cell where the failure occurs received fromthe LTE RRC message, that is, the base station identity of the gNB1.

The TAI is used for routing in the core network. For example, the AMFentity to which the ng-eNB1 is connected uses the TAI to find the AMFentity to which the gNB1 is connected, and forwards the information inthe uplink RAN configuration transfer message to the AMF to which thegNB1 is connected. The gNB1 and ng-eNB1 may be connected to the same AMFor different AMFs, and the AMF entity to which the ng-eNB1 is connectedknows whether the gNB1 and ng-eNB are connected to the same AMIEaccording to the TAI. Alternatively, the MME to which the eNB1 isconnected uses the TAI to find the AMF entity to which the gNB1 isconnected, and forwards the eNB configuration transfer message to theAMF to which the gNB1 is connected.

The identity of the base station which controls the cell where thefailure occurs is used for the core network to transmit a downlink RANconfiguration transfer message to the gNB1, otherwise the AMF does notknow to which base station the message may be transmitted.

The ng-eNB1 or the eNB1 does not need to decode the RLF report containerof the NR. This method may simplify the base station.

The ng-eNB1 or the eNB1 knows the cell that last serves the UE prior tothe failure directly according to the cell identity of the cell thatlast serves the UE before the failure occurs included in the LTE RRCmessage, and thus knows the base station which controls the cell, andtransmits a failure indication message to the base station. The ng-eNB1or the eNB1 may transmit a failure indication message to the basestation which controls the cell that last serves the UE prior to thefailure, without a support for implementing the RRC of the NR.Similarly, in the case where there is no Xn interface between theng-eNB1 and the gNB1 or there is no interface between the eNB1 and thegNB1, the ng-eNB1 or the eNB1 does not need to decode the content of theNR RLF report, and may know the TAI of the cell where the failure occursdirectly from the LTE RRC message, and know the base station identity ofthe base station which controls the cell where the failure occursaccording to the cell identity of the cell where the failure occurs, soas to transmit the RLF report to the gNB1 through the core network.Meanwhile, the UE does not need to wait to transmit the UE report untilthe UE reconnects to the NR base station, which reduces the time for theUE to store the RLF report and stores the UE's memory space. Similarly,in the case where there is no Xn interface between the ng-eNB1 and thegNB1 or there is no interface between the eNB1 and the gNB1, the ng-eNB1or the eNB1 does not need to decode the content of the NR RLF report,and may know the TAI of the cell where the failure occurs and/or thebase station identity of the base station which controls the cell wherethe failure occurs directly from the LTE RRC message, so as to transmitthe RLF report to the gNB1 through the core network.

Step 705: The AMF transmits a downlink RAN configuration transfer of theNGAP message to the gNB1. Here, other NGAP messages are possible to beused. The AMF knows the base station to which the message is to betransmitted according to the identity of the target base station.

Step 706: The gNB1 detects the cause of the failure occurring, such astoo early handover, too late handover, or handover to wrong cell. ThegNB1 may detect the cause of the failure occurring according to theexisting mechanism, and details are not described herein repeatedly.

For too early handover or handover to wrong cell, the gNB1 transmits ahandover report message to the base station which controls the sourcecell that triggers the last handover, such as the ng-eNB or the eNB1 orthe gNB. The gNB1 knows the identity of the source cell that triggersthe last handover according to the UE RLF report, and may thus know thebase station identity of the base station which controls the source cellthat triggers the last handover. The handover report message includesthe cell identity of the cell where the LTE attempts to establish theRRC connection, or the cell identity of the cell where the UEestablishes the RRC connection, after the failure. Optionally, thehandover report message may include the cell identity of the target cellfor the handover. If the base station that triggers the last handover isnot a base station supporting the NR access technology (e.g., the eNB orthe ng-eNB), the handover report may not include the UE RLF report. Thehandover report message directly includes a combination of one or moreof information as described in step 305. In this way, the eNB or theng-eNB may know more information about the failure without parsing theNR RRC information, so as to confirm the cause of the failure and makereasonable parameter adjustments to avoid future failures. The gNB1obtains the one or more information described in step 305 from the UERLF report, and the gNB1 makes one or more of the information directlyincluded in the handover report message, and sends the handover reportmessage to the base station which controls the source cell that triggersthe last handover. The gNB1 may makes one or more of the aboveinformation included in the handover report message in the case wherethe base station that triggers the last handover is not a base stationthat supports the NR radio access technology. In this way, the basestation that triggers the last handover may determine the cause of thefailure and make reasonable parameter adjustments to avoid futurefailures, without parsing the content in the UE RLF report in differentradio access technologies.

If there is no Xn interface or no interface between the gNB1 and thebase station which controls the source cell that triggers the lasthandover, the handover report needs to be transmitted through the corenetwork to the base station, the ng-eNB or the eNB1 or the gNB, whichcontrols the source cell that triggers the last handover.

The gNB1 transmits an uplink RAN configuration transfer of the NGAPmessage to the AMF. The TAI included in the message is set as the TAI ofthe source cell that triggers the last handover. The target base stationidentity is set as the base station identity of the base station whichcontrols the source cell that triggers the last handover. The messageincludes information about the too early handover or handover to wrongcell. The message may also be other NGAP messages. The gNB1 knows theTAI of the source cell that triggers the last handover according to theUE RLF report, and knows the base station identity of the base stationwhich controls the source cell that triggers the last handover accordingto the cell identity of the source cell that triggers the last handover.

Step 707: The AMF transmits a downlink RAN configuration transfer of theNGAP message to the ng-eNB or the gNB. For the case where the basestation that last triggers the handover is an LTE base station eNB, theMME transmits an MME configuration transfer of the S1AP message to theeNB. Here, other S1AP messages are possible to be used. The MME knowswhich base station the message is to be transmitted to, according to thetarget base station identity. The detailed description of the procedurebetween the AMF and the MME is omitted here.

So far, the description of the second embodiment of the first method forsupporting self-configuration and self-optimization of the presentdisclosure is completed. This method may enable the network to correctlydetect the cause of the failure in the case that the UE fails whenmoving between different RATs, while reducing the time for the UE tostore RLF report information and reducing the process on the basestation side, that is, the NR base station does not need to decode thecontent of the LTE RRC and the UE base station does not need to decodethe content of the NR RRC. When there is no Xn interface between thebase station which controls the cell where the failure occurs and thebase station which controls the cell where the UE reconnects, the LTEbase station may still transmit the RLF report to the base station whichcontrols the cell where the failure occurs through the core networkwithout parsing the NR RLF. When there is no Xn interface between thebase station which controls the cell where the failure occurs and thebase station which controls the cell that triggers the last handover,the base station which controls the cell where the failure occurs maystill transmit a handover report to the base station which controls thesource cell that triggers the last handover.

A first embodiment of the third method for supporting self-configurationand self-optimization according to the present disclosure is illustratedin FIG. 8 . A detailed description of steps which are not related to thepresent disclosure is omitted here. This embodiment is illustrated bytaking an example in which the failure occurs in an NR base station gNB,and the base station that the UE re-accesses after the failure is an LTEbase station ng-eNB. Conversely, this method may be applicable as well,for example, the failure occurs in the UE base station, the ng-eNB, andthe base station that the UE re-accesses after the failure is the NRbase station gNB.

The method includes steps as follows.

Step 801: A UE fails in a cell of the gNB1, and it is assumed that theUE fails in cell A. Herein, the failure may be an RLF or a handoverfailure. For the handover failure, the cell A is a target cell for thehandover. The cell where the failure occurs is also the cell that lastserves the UE prior to the failure. The UE stores one or more of thefollowing information:

-   -   Cell identity of the cell A, which may be a global cell identity        or a physical cell identifier (PCI) and frequency information;    -   Tracking area code (TAC) or tracking area identity (TAI) of the        cell A;    -   Cell identity of the source cell that triggers the last        handover;    -   Cell identity of the source cell that triggers the last        handover;    -   Time elapsed from the beginning of the last handover to the        failure;    -   Connection failure being an RLF or a handover failure;    -   Radio measurements of the UE;    -   C-RNTI allocated to the UE by the cell that last serves the UE        prior to the failure;    -   Cause of triggering an RLF;    -   Cell identity of the cell where the UE attempts to re-establish        the RRC connection after the failure;    -   Cell identity of the cell where the UE successfully establishes        the RRC connection, or cell identity of the cell where the UE        attempts to establish the RRC connection, after the failure;    -   Time elapsed from the failure to the UE RLF report;    -   Time elapsed from the failure to the RRC re-connection attempt        or successful access to the network. The RRC re-connection        attempt refers to transmission of an RRC connection        establishment request or RRC connection re-establishment request        message. The successful access to the network may be that the UE        transmits the RRC connection establishment completion or RRC        connection re-establishment completion or RACH success.

The last four items may be stored in a subsequent procedure. Forexample, when the UE attempts to re-establish the RRC connection, the UErecords the cell identity of the cell where the UE attempts tore-establish the RRC connection after the failure. When the successfullyre-establishes the RRC connection or the UE attempts to establish theRRC connection, the UE records the cell identity of the cell where theUE successfully establishes the RRC connection or the cell identity ofthe cell where the UE attempts to establish the RRC connection. When theprepares to transmit the RLF report, the UE records the time elapsedfrom the failure to the UE RLF report. Upon successful access to thenetwork, the UE records the time elapsed from the failure to successfulaccess to the network.

All the above cell identities may be the global cell identity or the PCIand the frequency information.

The UE also stores the RLF report of which radio access technology thestored RLF report information is, such as an LTE RLF report or an NR RLFreport.

The above-mentioned RLF report information is an NR RLF report, which isin a format and encoding of the NR RRC.

Step 802: The UE re-establishes the RRC connection in the cell of theng-eNB1 or the eNB1. The UE may re-establish the RRC connection throughthe RRC connection establishment or RRC connection re-establishmentprocedure. In the RRC connection establishment completion or RRCconnection re-establishment completion message, the UE indicates, to thenetwork, that the RLF report information is available.

Step 803: the UE is connected to the gNB2. The UE may access the gNB2through RRC connection establishment or RRC connection re-establishmentor handover. In the RRC connection establishment completion or RRCconnection re-establishment completion or RRC reconfiguration completionmessage, the UE indicates, to the network, the RLF report information isavailable. The RRC reconfiguration completion message is used toindicate that the handover completion. The UE may also indicate, to thenetwork, the RLF report information of which radio access technology isavailable, for example, in the present embodiment, the UE indicates tothe network the NR RLF report is available.

The method of the present disclosure may further include the step ofbroadcasting, by the base station, whether the base station supports theRLF information reporting. If the base station with which the UEre-establishes the RRC connection supports the RLF informationreporting, the UE transmits, to the re-accessed base station, the RLFinformation reporting is available. For example, the gNB2 broadcastswhether the gNB2 supports the RLF information reporting, the UEre-accesses the gNB2, and the UE may indicate, to the gNB2, the RLFinformation report is available.

The UE stores that the RLF report information is the RFL report of whichradio access technology, for example, the LTE stores the NR RLF report,and when the UE re-accesses the NR base station, the UE indicates, tothe gNB2, the RLF report information is available.

Step 804: The gNB2 requests the UE to report the RLF report, and the UEtransmits a UE RLF report to gNB2.

Step 805: The UE RLF report includes the content described in step 801.The gNB2 knows the base station gNB1 which controls the cell where thefailure occurs, according to the cell identity of the cell that lastserves the UE before the failure occurs included in the UT RLF report.The gNB2 transmits a failure indication message to the gNB1. The failureindication message includes the RLF report received from the UE.

If there is no Xn interface between the gNB2 and the gNB1, the gNB2needs to transmit the RLF report to the gNB1 through the core network.

The gNB2 transmits an uplink RAN configuration transfer of an NEAPmessage to the AMF. Here, other NGAP messages are possible to be used.The message includes the UE RLF report, the TAI of the cell where thefailure occurs and the base station identity of the base station whichcontrols the cell where the failure occurs. The gNB3 sets the identityof the target base station in the message as the base station identityof the base station which controls the cell where the failure occurs.The gNB3 sets the target TAI in the message as the TAI of the cell wherethe failure occurs. The gNB2 knows the TAI of the cell where the failureoccurs from the cell identity and the TAC or TAI of the cell where thefailure occurs included in the UE RLF report. The gNB2 knows the basestation identity of the base station which controls the cell where thefailure occurs, from the cell identity of the failed cell included inthe UE RLF report. The TAI is used for routing in the core network, forexample, the core network entity (such as AMF2) to which the gNB2 isconnected finds the core network entity (such as AMF1) to which the gNB1is connected. The gNB1 and the gNB2 may also be connected to the sameAMF. That is, AMF1 and AMF2 may be the same AMF or different AMFs. Thebase station identity is used for the AMF to forward the UE RLF reportto the base station gNB1 of the cell where the failure occurs.

Step 806: The AMF transmits a downlink RAN configuration transfer of theNGAP message to the gNB1. Here, other NGAP messages are possible to beused. The message includes the UE RLF report. The AMF knows which basestation the message is to be transmitted to, according to the identityof the target base station.

Step 807: The gNB1 detects the cause of the failure occurring, such astoo early handover, too late handover, or handover to wrong cell. ThegNB1 knows the right cell to which the UE may be handed over accordingto the cell identity of cell where the UE successfully establishes theRRC connection or the cell identity of cell where the UE attempts toestablish the RRC connection, after the failure. For the too latehandover, the failed cell may handover the UE to the cell where the UEsuccessfully establishes the RRC connection or the cell where the UEattempts to establish the RRC connection. For the too early handover orthe handover to wrong cell, the source cell that triggers the lasthandover may handover the UE to the cell where the UE attempts toestablish the RRC connection or the cell where the UE successfullyestablishes the RRC connection. The gNB1 may also determine whether thecell where the LTE attempts to establish the RRC connection or the cellwhere the UE successfully establishes the RRC connection after thefailure is a suitable handover cell of the handover according to thetime elapsed from the failure to the RRC re-connection attempt or thesuccessful access to the network.

For the too early handover or the handover to wrong cell, the gNB1transmits a handover report message to the base station which controlsthe source cell that triggers the last handover, such as the ng-eNB orthe eNB or the gNB. The gNB1 knows the identity of the source cell thattriggers the last handover according to the UE RFL report, and thus mayknow the identity of the base station which controls the source cellthat triggers the last handover. The handover report message includesthe cell identity of the cell where the UE attempts to establish the RRCconnection or the cell identity of the cell where the UE establishes theRRC connection, after the failure. Optionally, the handover reportmessage may include the cell identity of the target cell for thehandover. If the base station that triggers the last handover is not abase station that supports the NR access technology (for example, theeNB or the ng-eNB), the handover report may not include the UE RFLreport. The handover report message directly includes a combination ofone or more of the information described in step 305. In this way, theeNB or the ng-eNB may know more information about the failure withoutparsing the NR RRC information, so as to confirm the cause of thefailure and make reasonable parameter adjustments to avoid futurefailures. The gNB1 obtains the one or more information described in step305 from the UE RLF report, and the gNB1 makes one or more of theinformation directly included in the handover report message, and sendsthe handover report message to the base station which controls thesource cell that triggers the last handover. The gNB1 may makes one ormore of the above information included in the handover report message inthe case where the base station that triggers the last handover is not abase station that supports the NR radio access technology. In this way,the base station that triggers the last handover may determine the causeof the failure and make reasonable parameter adjustments to avoid futurefailures, without parsing the content in the UE RLF report of differentradio access technologies.

If there is no interface between the gNB1 and the base station whichcontrols the source cell that triggers the last handover, the handoverreport needs to be transmitted through the core network to the basestation, the ng-eNB or the eNB or the gNB, which controls the sourcecell that triggers the last handover.

The gNB1 transmits an uplink RAN configuration transfer of the NGAPmessage to the AMF. The TAI included in the message is set as the TAI ofthe source cell that triggers the last handover. The target base stationidentity is set as the identity of the base station which controls thesource cell that triggers the last handover. The message includesinformation about the too early handover or the handover to wrong cell.The message may also be other NGAP messages. The gNB1 knows the TAI ofthe source cell that triggers the last handover according to the UE RLFreport, and knows the identity of the base station which controls thesource cell that triggers the last handover according to the cellidentity of the source cell that triggers the last handover.

Step 808: The AMF transmits a downlink RAN configuration transfer of theNGAP message to the ng-eNB or the gNB. For the case where the basestation that last triggers the handover is an UE base station eNB, theMME transmits an MME configuration transfer of the S1AP message to theeNB. Here, other S1AP messages are possible to be used. The MME knowswhich base station the message is to be transmitted to, according to thetarget base station identity. The detailed description of the procedurebetween the AMF and the MME is omitted here.

So far, the description of the embodiment of the third method forsupporting self-configuration and self-optimization of the presentdisclosure is completed. This method may enable the network to correctlydetect the cause of the failure in the case that the UE fails whenmoving between different RATs, while reducing the process on the basestation side, that is, the NR base station does not need to decode thecontent of the LTE RRC and the LTE base station does not need to decodethe content of the NR RRC. When there is no Xn interface between thebase station which controls the cell where the failure occurs and thebase station which controls the cell where the UE reconnects, the NRbase station may still transmit the RLF report to the base station whichcontrols the cell where the failure occurs through the core networkwithout parsing the NR RLF. When there is no Xn interface between thebase station which controls the cell where the failure occurs and thebase station which controls the cell that triggers the last handover,the base station of the cell where the failure occurs may still transmitthe handover report to the base station which controls the source cellthat triggers the last handover.

So far, the description of the method for supporting self-configurationand self-optimization of the present disclosure is completed. Thismethod may enable the network to correctly detect the cause of thefailure in the case that the UE fails when moving between differentRATs, while reducing the time for the UE to store RLF report informationand reducing the process on the base station side, that is, the NR basestation does not need to decode the content of the LTE RRC and the LTEbase station does not need to decode the content of the NR RRE. Whenthere is no Xn interface between the base station which controls thecell where the failure occurs and the base station which controls thecell where the UE reconnects, the base station may still transmit theRLF report to the base station which controls the cell where the failureoccurs through the core network without parsing the RLF of other radioaccess technologies. When there is no Xn interface between the basestation which controls the cell where the failure occurs and the basestation which controls the cell that triggers the last handover, thebase station of the cell where the failure occurs may still transmit ahandover report to the base station which controls the source cell thattriggers the last handover.

FIG. 9 is a block diagram of a terminal according to an embodiment ofthe present disclosure.

Referring to FIG. 9 , the terminal includes a transceiver 910, acontroller 920, and a memory 930. The transceiver 910, the controller920, and the memory 930 are configured to perform operations of the UEshown in FIGS. 3 to 8 or described above. Although the transceiver 910,the controller 920, and the memory 930 are shown as separate entities,the transceiver 910, the controller 920, and the memory 930 may beimplemented as a single entity, such as a single chip. The transceiver910, the controller 920, and the memory 930 may be electricallyconnected or coupled to each other. The transceiver 910 may transmitsignals to and receive signals from other network entities, such as abase station. The controller 920 may control the HE to perform afunction according to one of the above embodiments. For example, thecontroller 920 is configured to store, by the UE, information about thefailure when the UE fails in a first cell; establish, by the UE, aconnection with a second base station of a second cell; receive, by theUE, a request message for reporting a failure report from the secondbase station; and transmit, by the UE, to the second base station amessage about the failure report, the message about the failure reportincludes a UE RLF report container, and the UE RLF report containerincludes identity information about the cell where the failure occursand/or information of tracking area of the cell where the failureoccurs.

FIG. 10 is a block diagram of a base station according to an embodimentof the present disclosure.

Referring to FIG. 10 , the base station includes a transceiver 1010, acontroller 1020, and a memory 1030. The transceiver 1010 the controller1020, and the memory 1030 are configured to perform operations of thenetwork base station shown in FIGS. 3 to 8 or described above. Althoughthe transceiver 1010, the controller 1020, and the memory 1030 are shownas separate entities, the transceiver 1010, the controller 1020, and thememory 1030 may be implemented as a single entity, such as a singlechip. The transceiver 1010, the controller 1020, and the memory 1030 maybe electrically connected or coupled to each other. The transceiver 1010may transmit signals to and receive signals from other network entities,such as a UE. The controller 1020 may control the base station toperform a function according to one of the above embodiments. Forexample, the controller 1020 is configured to establish, by a secondbase station of a second cell, a connection with the terminal after theUE fails in a first cell; transmits, by the second base station, to theUE a request message of reporting the failure report, the requestmessage includes information about the failure stored by the terminal;receive, by the second base station, a message about the failure reportfrom the UE, the message about the failure report includes a UE RLFreport container, the UE RLF report container includes identityinformation about the cell where the failure occurs and/or informationof tracking area of the cell where the failure occurs.

Although the present disclosure has been described with variousembodiments, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method performed by a first base stationoperating according to a first radio access technology (RAT) in awireless communication system, the method comprising: transmitting, to aterminal, a request message including information indicating that theterminal reports failure report information related to a connectionfailure; as a response to the request message, receiving, from theterminal, a response message including an identity of a cell in whichthe connection failure has occurred and a failure report containercontaining the failure report information, the cell being controlled bya second base station operating according to a second RAT; andtransmitting, to a core network entity, an uplink radio access network(RAN) configuration transfer message including an identity of the secondbase station and the failure report container, wherein, in the uplinkRAN configuration transfer message, the identity of the second basestation is included outside the failure report container.
 2. The methodof claim 1, wherein the uplink RAN configuration transfer messagefurther includes a tracking area code (TAC) of the cell.
 3. The methodof claim 1, wherein the failure report, container is transparentlytransferred towards the second base station.
 4. The method of claim 1,wherein, in the response message, the identity of the cell is includedoutside the failure report container.
 5. The method of claim 1, whereinthe identity of the cell is a global cell identity.
 6. A methodperformed by a core network entity in a wireless communication system,the method comprising: receiving, from a first base station operatingaccording to a first radio access technology (RAT), an uplink radioaccess network (RAN) configuration transfer message including anidentity of a second base station controlling a cell in which aconnection failure of a terminal has occurred and a failure reportcontainer containing failure report information related to theconnection failure; identifying the second base station based on theidentity of the second base station included in the uplink RANconfiguration transfer message; and transferring, to the second basestation, the failure report container, wherein, in the uplink RANconfiguration transfer message, the identity of the second base stationis included outside the failure report container.
 7. The method of claim6, wherein the uplink RAN configuration transfer message furtherincludes a tracking area code (TAC) of the cell.
 8. The method of claim6, wherein the failure report container is transparently transferredtowards the second base station.
 9. A first base station operatingaccording to a first radio access technology (RAT) in a wirelesscommunication system, the first base station comprising: a transceiver;and a controller configured to: transmit, to a terminal via thetransceiver, a request message including information indicating that theterminal reports failure report information related to a connectionfailure, as a response to the request message, receive, from theterminal via the transceiver, a response message including an identityof a cell in which the connection failure has occurred and a failurereport container containing the failure report information, the cellbeing controlled by a second base station operating according to asecond RAT, and transmit, to a core network entity via the transceiver,an uplink radio access network (RAN) configuration transfer messageincluding an identity of the second base station and the failure reportcontainer, wherein, in the uplink RAN configuration transfer message,the identity, of the second base station is included outside the failurereport container.
 10. The first base station of claim 9, wherein theuplink RAN configuration transfer message further includes a trackingarea code (TAC) of the cell.
 11. The first base station of claim 9,wherein the failure report container is transparently transferredtowards the second base station.
 12. The first base station of claim 9,wherein, in the response message, the identity of the cell is includedoutside the failure report container.
 13. The first base station ofclaim 9, wherein the identity of the cell is a global cell identity. 14.A core network entity in a wireless communication system, the corenetwork entity comprising: a transceiver; and a controller configuredto: receive, from a first base station operating according to a firstradio access technology (RAT) via the transceiver, an uplink radioaccess network (RAN) configuration transfer message including anidentity of a second base station controlling a cell in which aconnection failure of a terminal has occurred and a failure reportcontainer containing failure report information related. to theconnection failure, identify the second base station based on theidentity of the second base station included in the uplink RANconfiguration transfer message, and transfer, to the second base stationvia the transceiver, the failure report container, wherein, in theuplink RAN configuration transfer message, the identity of the secondbase station is included outside the failure report container.
 15. Thecore network entity of claim 14, wherein the uplink RAN configurationtransfer message further includes a tracking area code (TAC) of thecell.
 16. The core network entity of claim 14, wherein the failurereport container is transparently transferred towards the second basestation.